docs: Integration the injection part in the docs rendering

docs/Makefile

@@ -4,6 +4,7 @@ html: copy_md
 
 copy_md:
 	cp ../README-getting-started.md getting-started.md
-	cp ../README.md spec-info.md
+	cp ../README.md spec-api.md
+	cp ../README-injection.md spec-injection.md
 	cp ../README-dev.md dev-info.md
 	cp ../README-sys.md sys-info.md

docs/index.rst

@@ -6,7 +6,8 @@ Software Heritage Deposit
    :caption: Contents:
 
    getting-started.md
-   spec-info.md
+   spec-api.md
+   spec-injection.md
    dev-info.md
    sys-info.md