website: use sentence case in Sapling docs headings

Summary:
Historically, we use "Foo bar", not "Foo Bar", title.

https://developers.google.com/style/capitalization

Update non-generated Sapling docs headings and sidebar labels to use sentence
case while preserving proper nouns.

Reviewed By: genevievehelsel

Differential Revision: D104288661

fbshipit-source-id: 8b7310614665a35601a678005a3d08276eb68acd

Author: quark-zju

website/docs/addons/isl.md

@@ -4,7 +4,7 @@ sidebar_position: 10
 
 import {Video, Command, SLCommand, ThemedImage} from '@site/elements'
 
-# Interactive Smartlog (ISL)
+# Interactive smartlog (ISL)
 
 Interactive Smartlog (ISL) is a web-based, graphical interface for working with your Sapling smartlog. It is available as part of Sapling Web, which you can launch from the command line as follows:
 

website/docs/dev/_category_.json

@@ -1,4 +1,4 @@
 {
-  "label": "Developer Guide",
+  "label": "Developer guide",
   "position": 7
 }

website/docs/dev/index.md

@@ -1,4 +1,4 @@
-# Sapling Developer Guide
+# Sapling developer guide
 
 This is a Work-In-Progress! Content below might be rewritten entirely.
 

website/docs/dev/internals/copytracing.md

@@ -1,4 +1,4 @@
-# Bisect-Based Copy Tracing
+# Bisect-based copy tracing
 
 *Copy tracing* is a technique used to efficiently account for file copies and
 renames when comparing histories. It is used for `diff` commands and merge-related
@@ -83,7 +83,7 @@ Bisect-based copy tracing is built to achieve the following desired properties:
 - **Abstracted**: Support both Sapling and Git backend repositories.
 - **Efficiency**: Provides fast content similarity checks for cases where renames
   are not recorded in Sapling or when working with Git repositories.
-- **User-Friendly**: Informative message when renames cannot be found, such as
+- **User-friendly**: Informative message when renames cannot be found, such as
   delete/modified conflicts.
 
 ## How?
@@ -118,7 +118,7 @@ where N is the line count (`O(N^2)` is the worst case for the Myers diff algorit
 Our approach, `xdiff::edit_cost`, imposes a `max cost` limit, reducing the
 complexity to `O(N)`.
 
-### User-Friendly
+### User-friendly
 When renames cannot be found, for example, file `a.txt` was renamed to `a.md`
 and then deleted on the destination branch, the new copy tracing can identify
 both the commit that renamed the file and also the commit that eventually

website/docs/git/_category_.json

@@ -1,5 +1,5 @@
 {
-  "label": "Git Interop",
+  "label": "Git interop",
   "position": 4,
   "link": {
     "type": "generated-index",

website/docs/git/signing.md

@@ -4,11 +4,11 @@ sidebar_position: 4
 
 import {SLCommand} from '@site/elements'
 
-# Signing Commits
+# Signing commits
 
 Currently, signing is only supported with commits in Git repos. See [Git's documentation on "Signing Your Work" for more context](https://git-scm.com/book/en/v2/Git-Tools-Signing-Your-Work). Sapling supports GPG, SSH, and X.509 (S/MIME) signing backends.
 
-## Identity Configuration (GPG)
+## Identity configuration (GPG)
 
 When using GPG signing, Sapling has a single configuration for your identity:
 

website/docs/overview/smartlog.md

@@ -64,7 +64,7 @@ o  <span class="sl-public">a75ab860a</span>  Jul 15 at 07:59<br />
 ~<br />
 </pre>
 
-### Super Smartlog
+### Super smartlog
 
 Sapling can also fetch information about the repository from external sources, such as checking GitHub to know if a pull request has passed automated tests and been reviewed. Since this extra information requires waiting a few seconds for network requests, we have a separate <SLCommand name="ssl" /> alias for this:
 

website/docs/scale/_category_.json

@@ -1,5 +1,5 @@
 {
-  "label": "Working at Scale",
+  "label": "Working at scale",
   "position": 6,
   "link": {
     "type": "generated-index"

website/docs/scale/overview.md

@@ -35,7 +35,7 @@ failures, we back up all commits as they are created to our "commit cloud".
 Unlike other systems, the developer doesn't have to expressly push their
 commits for them to be shareable and durable.
 
-## Note about "Distributed"
+## Note about "distributed"
 
 Sapling started from Mercurial as a distributed source control system, it then
 transitioned to a client-server architecture to solve the challenges.